Patent GB-594143-A (GB)
Title: Screwthread cutting mechanism
IPC: B23G5/14
Filed: 1945-01-30
Abstract: 594,143. Screwing die-heads ; taps. LANDIS MACHINE CO. Jan. 30, 1945, No. 2377. Convention date, Feb. 23, 1944. [Class 83 (iii)] In a taper threading screwing diehead or tap wherein the chasers are moved radially during cutting and are retracted rapidly from the work at the end of the cutting operation, the chasers are operated by an axially sliding plunger which is in two relatively movable parts so that the movable part controls the chasers. to produce the tapered thread and the other part is latched to the body of the tool to be released when threading is completed. As applied to a tap, the body 10 receives radially sliding chasers 20 which are moved positively in both directions by inclined keyways on a core 23 attached by a rod 30 to the two-part plunger 28, 29 coaxial with the core. A sleeve 12 on the body 10 is adjustably connected by studs 15 to a collar 14 adapted to engage the work &c. and is splined to the body by a key 106, Fig. 4. A rectangular housing 61 on the sleeve 12 carries an adjustable sliding. pivot 69 for a lever 48 carrying two pins 49, 50, whereof the former engages a transversely slidable block 47 in an extension 40 of the plunger 28 whilst the latter engages a key 52 in a recess of the extension 43 of the plunger 29. A spigot 45 on plunger 29 slides in a sleeve 87 secured in the body 10 by a screw 90, the forward end of the sleeve serving as a stop for a U-shaped latch 84 transversely slidable in a recess in the spigot and pressed outwardly by a spring 85. Operation. With the plunger 29 latched in the forward position and the sleeve 12 in its forward position, as shown in Fig. 1, when the chasers commence cutting the collar 14 engages the end of the work or other stationary part so as to cause the sleeve to be pushed back on the body duxing screwing. This rocks the lever 48 clockwise in Fig. 1 about the pivot 50 and the pin 49 retracts the plunger 28 to withdraw the chasers slowly from the work to produce the taper thread. On completion of the cutting operation, a cam bar 100, Fig. 4, on the sleeve engages by its inclined surface 101 with a radially slidable pin 93 in the body, thereby depressing the pin and disengaging the latch 84 from the sleeve 87. This allows a spring 75, attached by its end convolutions to a stud on plunger 29 and a nut 79 secured to the body by a, screw 80, to withdraw the plungers 28, 29 rapidly, as shown in Fig. 4, thereby actuating the core 23 to collapse the chasers. The length of thread cut is determined by locking the bar 100 in adjusted position on the sleeve 12 by screws 104, and the bar may be turned end for end to make use of a differently spaced incline 102. The latch sleeve 87 may be adjusted. angularly in the body by the screw 90 and a series of holes 88 therein, or may be turned end for end, when the surface engaging the latch 84 becomes worn. Re-setting. To re-set the chasers the sleeve 12 is moved forward on the body by a yoke or by gravity, if the tap is vertical, thereby restoring the sleeve and lever 48 to a forward position and bringing pins 57 on the sleeve into contact with the key 52. A hand lever 109, Fig. 4, is then in position to engage a toothed segment 110 thereon with rack teeth 108 on the stationary key 106 so that clockwise rocking of the lever will cause the pins 57 to draw the plunger 29 forwards, through the key 52, until the latch 84 snaps over the sleeve 87 to lock the chasers in cutting position as shown in Fig. 1. Alternatively, pressure may be applied directly to the sleeve 12 for this final movement. Taper-determining. The angle of taper produced on the work is varied by adjusting the distance of the pivot 69 on the lever 48 from the fulcrum 50. For this purpose the pivot is carried by a block 68 and engages semicylindrical pads 70 slidable in a bore 63 of the housing 61. The block is provided with one or more differently spaced notches 74 in each of its sides so that by removing the block and rotating it through one or more right angles, the required notch may be engaged with a projection 73 on the lever, the setting being indicated by a graduated scale on the lever reading against the lower edge of the block. Set-position, determining. The wedge core 23 has screwed engagement with the stud 30 which is attached to the plunger 28 by collars 33 and a flange 35 on the plunger so that rotation of the stud will adjust the chasers for diameter of cut, locking being effected by a serrated pad 36 and a spring 37 in the plunger. Specifications 548,303 and 551,554 are referred to.